**2. Climate and soil in the southern Green belt of Buenos Aires**

The climate is mild without a dry season, with hot summers and mild winters. The average annual temperature is 16°C and the frost-free period is of 220 days (from October 20 to May 10). With the expansion of greenhouses, the influence of climatic conditions has diminished, however, the extreme temperature, high air relative humidity and the excess or deficit of light represent climatic limits for this production system. The total rainfall in the area is between 900 and 1000 mm a year and is distributed more or less uniformly in the four seasons. The water used for irrigation is extracted from between 55 and 60 m deep in each farm [1]. Generally the irrigation system is drip irrigation (20 cm between drippers, with two irrigation hoses per spine) and fertilization is performed by fertirrigation [8].

With respect to geomorphology, the southern green belt is characterized by gentle undulations of long and not very steep slopes. The area that encompasses the southern urban and peri-urban area is crossed by streams that run through it and drain into two basins: the Río de la Plata and the Samborombón and the Salado rivers. Between these basins there is a quite elevated terrain that separates their drainage.


The types of soil that predominate vary with the origin of their primary materials. In the higher areas, lithologically, the original materials belong mostly to the

*BD: bulk density by cylinder method [15]; AS (MWD): aggregate stability (mean weight diameter) [16]; Soil texture: clay, sand and silt percentage (USDA triangle); pH and EC: electrical conductivity in water 1.2.5 by potentiometry [17]; TOC: total oxidative carbon by Walkley and Black [18]; MOC: oxidative carbon associated with the mineral fraction; POC: particulate oxidative carbon [19]; TN: total nitrogen by Kjeldahl micro-method [20]; and EP: extractable phosphorus by Bray and Kurtz 1 [20].*

#### **Table 1.**

*Peri-urban soils characteristic in non-cultivated sites.*

*Urban Horticulture - Necessity of the Future*

carried out in every province of Argentina, it has importance from a geopolitical

*(a) Argentinian horticultural regions. (b) Buenos Aires metropolitan districts that integrate de Green belt. References indicate the number of farmers per district. Source: [1] and Censo Hortiflorícola de Buenos Aires [4] Ministerio de Asuntos Agrarios—PBA. The boxed area indicated the sampling area (Florencio Varela and La* 

The wide distribution of horticulture in Argentina is due in part to the diversity of climates that it possesses, however the commercial production that supplies the main urban centers with fresh vegetables is located in the peripheral area of those urban centers (peri-urban). The peri-urban is represented by an area of small farms and orchards in the surrounding of large cities, which production is specialized in leafy vegetables and seasonal vegetables. Therefore this area is commonly referred to as the "green belt" [3]. The green belt of Buenos Aires city has more than 5.510 km2 and includes a population of more than 4.5 million habitants. This area is represented by the districts of La Plata, Florencio Varela, Berazategui, Almirante Brown, Esteban Echeverría, La Matanza, Merlo, Moreno, Cañuelas, General Rodríguez, Luján, Marcos Paz, Pilar and Escobar. The three most important districts in terms of horticulture are in the southern peri-urban of Buenos Aires city (La Plata, Berazategui and Florencio Varela) (**Figure 1**). These districts represent 82% of the total horticultural farms and 81% of the surface under cultivation [5]. This is one of the most important areas for fresh food production (refer to leafy vegetables or flowers, fruits and stems); therefore, horticulture is very important in the local economy. Horticulture in the southern green belt of Buenos Aires city is characterized by having an intensive and highly diversified production scheme in terms of production systems and diversity of species cultivated. The largest area in hectares is under open-field cultivation systems, however most producers have a combination of both open-field and greenhouse cultivation systems. The total area of the southern green belt under vegetables production is 5332.8 ha, with 30% under greenhouses cultivation systems and the rest in open-field cultivation systems [4]. Although there is a marked heterogeneity of producers, small and medium-sized enterprises, mainly from family farming, stands out. However, there are also a small number of business-type productions with mainly hired labor. Approximately 70% of producers rent small areas of land (smaller than 5 ha) and can have 1–1.5 ha under greenhouses [6]. Only half of the producers have technical advice mostly from

and strategic point of view, being part of the "regional economies" [1].

**118**

*Plata).*

**Figure 1.**

"pampean sediment" consisting of sand-clay silt with limestone (loess). However, the limestone is not present in the upper horizons due to washing. Properties as pH, organic matter and soluble salts make these soils suitable for agriculture. In addition, due to their topographic condition they are not affected by floods [9]. Most agricultural soils in the southern green belt belong to the Molisol and Vertisol orders [10] (Chernozems and Vertisols) [11]. They have a strong profile development with dark A horizons, generally thick and well provided with organic matter followed by B horizons enriched in eluviated clay accompanied, especially in Vertisols, by evidence of expansion and contraction of materials. These are soils with high cation exchange capacity given by both organic matter and clay content. From the physical point of view, high levels of clay and silt, makes them susceptible to changes in their physical properties. In some cases there is low permeability and high plasticity in B horizons.

Low permeability is the main physical limitation for soils management in this area being more pronounced in the district of La Plata, where Vertisols with high clay content in surface (between 32 and 40%) and depth (50–60%), prevail. The only chemical limitation is low P content (less than 10 mg kg<sup>−</sup><sup>1</sup> ) [12]. However, [9] reported 20.7 mg kg<sup>−</sup><sup>1</sup> in soils from natural fields. Moreover, [13, 14] studying the surroundings of La Plata reported levels of extractable P greater than 20 mg kg<sup>−</sup><sup>1</sup> in soils that were not under agriculture for at least the past 20 years. **Table 1** describes some physical and chemical properties of soils around the houses of horticultural farmers from the southern green belt of Buenos Aires city.
